In the field of digital communications, there are extensive application requirements for transmission of speeches, images, audios, and videos, such as mobile phone calls, audio/video conferencing, broadcast television, and multimedia entertainment. A speech is digitized, and then transferred from one terminal to another terminal through a voice communication network. Herein the terminals may be mobile phones, digital phone terminals, or voice terminals or any other types. Examples of digital phone terminals are Voice over Internet Protocol (VoIP) phones or Integrated Services Digital Network (ISDN) phones, computers, and cable communication phones. To reduce resources occupied in the process of storing or transmitting audio signals, a sending end performs compression processing on audio signals before transmitting the audio signals to a receiving end, and the receiving end performs decompression processing to restore the audio signals and play the audio signals.
In voice communication, speech is included in only about 40% of the time, and at other times, there is only silence or background noise. To save transmission bandwidths and avoid unnecessary consumption of bandwidths in a silence or background noise period, a Discontinuous transmission system/Comfort Noise Generation (DTX/CNG) technology emerges. Simply, DTX/CNG means not encoding noise frames continuously, but performing encoding only once at an interval of several frames in a noise/silence period according to a policy, where an encoded bit rate is generally much lower than a bit rate of speech frame encoding. A noise frame encoded at such a low rate is referred to as a Silence Insertion Descriptor frame (SID). A decoder restores continuous background noise frames at the decoding end according to discontinuously received SIDs. Such continuously restored background noise is not a faithful reproduction of background noise of an encoding end, but aims to avoid causing quality deterioration in hearing as much as possible, so that a user feels comfortable when hearing the noise. The restored background noise is referred to as Comfort Noise (CN), and the method for restoring the CN at the decoding end is referred to as comfort noise generation.
In the prior art, International Telecommunications Union Telecommunication Standardization Sector (ITU-T) G.718 is a new standard wideband codec, which includes a wideband DTX/CNG system. The system may send a SID according to a fixed interval, and may also adaptively adjust the SID sending interval according to an estimated noise level. A SID frame of G.718 includes 16 immittance spectral pair (ISP) parameters and excitation energy parameters. This group of ISP parameters represents a spectral envelope on the bandwidth of an entire wide band, and an excitation energy is obtained by an analysis filter represented by this group of ISP parameters. At the decoding end, the G.718 estimates, according to ISP parameters obtained by decoding a SID in a CNG state, a linear prediction coefficient (LPC) required for CNG, estimates, according to excitation energy parameters obtained by decoding the SID frame, an excitation energy required for CNG, and uses gain-adjusted white noise to excite a CNG synthesis filter to obtain a reconstructed CN.
However, for a super-wideband spectral envelope, the bandwidth of the super wide band is extremely wide; when the prior art is extended to a super-wideband DTX/CNG system, more calculation loads and bits need to be consumed to calculate and encode the added dozen of ISP parameters, because a complete super-wideband spectral envelope needs to be encoded for a SID. Because high-band signals of noise (which refers to a frequency range above the wide band herein) are generally not perceptually sensitive in hearing, calculation loads and bits consumed for this part of signals are not cost-effective, thereby reducing the encoding efficiency of the codec.